Polysiloxane compositions are excellent in heat resistance, cold resistance, weather resistance, light resistance, chemical stability, electric characteristics, flame retardancy, water resistance, transparency, coloring properties, non-adhesiveness, and non-corrosiveness, and are used in various industries, and silica is generally mixed as a filler. However, resultant cured products are often opaque due to a difference in refractive index between silica and polysiloxane.
In order to resolve the problem, there is known a technique of introducing a phenyl group on a Si atom of a polysiloxane to control the refractive index thereof, thereby improving transparency of a composite material with silica. However, a composite material of a polysiloxane and silica is transparency, for example, at room temperature but tends to be clouded under high-temperature conditions due to a difference in temperature dependency of refractive index between the polysiloxane and silica. Therefore, to maintain transparency over a wide temperature region has been a large problem. In addition, there has been a problem of decreasing heat resistance and light resistance by introducing a phenyl group.
On the other hand, resin compositions characterized by containing a polysiloxane having a polyhedral skeleton are known.
For example, a hydrosilylated curable composition of functional group-containing silsesquioxane having a polyhedral skeleton is disclosed. In this technique, specifically, an example composed of vinyl group-containing silsesquioxane and hydrosilyl group-containing silsesquioxane is disclosed. However, the resultant material is rigid and quite brittle and has low molding workability (for example, Non-patent Document 1).
Also a resin composition containing silsesquioxane having a polyhedral skeleton having a carbon-carbon double bond and a radical initiator is disclosed (Patent Document 1). In this technique, a polysiloxane compound having a polyhedral skeleton is used as an additive for a thermoplastic resin, and the characteristics thereof are not sufficiently exhibited. In addition, the polysiloxane compound is not a matrix component, and thus the improving effect remains limited.
Further, a curable composition using a polysiloxane having a polyhedral skeleton containing an epoxy group has recently been disclosed (Patent Documents 2 and 3). In this technique, there is many hydrocarbon units (spacer composed of an alkylene chain) between an epoxy group and a polysiloxane skeleton which forms the polyhedral skeleton, and thus heat resistance and light resistance are not sufficient.
Further, a hybrid material including silsesquioxane having a specified structure and a polysiloxane is disclosed as an example not having a polyhedral skeleton (Patent Document 4). In this technique, substantially, one silsesquioxane unit is bonded at only two reaction points to a linear polysiloxane, thereby failing to achieve sufficient characteristics. Further, substantially only a phenyl group is disclosed as a substituent on a Si atom which constitutes a polysiloxane skeleton, and thus the material may be unsatisfactory from the viewpoint of heat resistance and light resistance.
Further, a copolymer produced by reaction between silsesquioxane having a polyhedral skeleton and a vinyl group-containing compound is disclosed. In this technique, the copolymer has a structure in which silsesquioxane having a polyhedral skeleton is grafted onto a polymer constituting a main chain, and exhibits a certain improving effect. However, the effect may be unsatisfactory (for example, Patent Document 5).
Although these polysiloxane compositions have the problems of a high coefficient of thermal expansion and low thermal dimensional stability, a resin composition composed of a polysiloxane having a polyhedral skeleton containing an epoxy group and an amino group is also disclosed. It is reported that the coefficient of thermal expansion can be suppressed by introducing a polysiloxane having a polyhedral skeleton into a resin composition (Patent Document 6 and Non-patent Document 2). However, in this technique, the composition includes many hydrocarbon units containing an epoxy group, an amino group, and a phenylene group, and coloring occurs due to heating or light irradiation. Therefore, the composition may become insufficient for use as a transparent material for films, sealants, and the like. Namely, there has been found no example of a material maintaining transparency and having excellent thermal dimensional stability and a low coefficient of thermal expansion.
In addition, a short-wavelength laser called a blue-violet laser (a wavelength of about 405 nm) has recently been used in large-capacity recording media such as next-generation DVD. Since the blue-violet laser has high energy as compared with a red laser (a wavelength of about 650 nm) generally used for DVD and the like, deterioration in a resin used for an optodevice becomes a large problem.
As a resin having blue-violet laser resistance, for example, cycloolefin resins and acrylic resins (for example, Non-patent Document 3, Patent Document 7, and Patent Document 8) and silicone resins (for example, Patent Document 9) have been disclosed. However, durability is not sufficient.
As described above, materials each including a polysiloxane compound having a polyhedral skeleton have been disclosed. However, there has been found no example of a material having sufficient physical properties, workability, and moldability, and thus development of a new material has been demanded.
[Non-patent Document 1] J. Am. Chem. Soc. 1998, 120, 8380-8391
[Non-patent Document 2] Macromolecules, 2006, 39, 5167-5169
[Non-patent Document 3] Journal of the Society of Rubber Industry, Japan, 2006, Vol. 79, No. 4, 244
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2002-363414
[Patent Document 2] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No.
[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2004-359933
[Patent Document 4] Japanese Unexamined Patent Application Publication No. 2006-22207
[Patent Document 5] U.S. Pat. No. 5,484,867 specification
[Patent Document 6] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No.
[Patent Document 7] Japanese Unexamined Patent Application Publication No. 2004-204018
[Patent Document 8] Japanese Unexamined Patent Application Publication No. 2003-270401
[Patent Document 9] Japanese Unexamined Patent Application Publication No. 2006-202952